Clickity clack noise

[belopsky]

Anyone know? Seems to be coming from right cylinder only..

https://www.facebook.com/video.php?v=10 ... 8170467251" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

I took the top end off, right side only, to investigate..ripped base gasket in process..

The pistons are .5mm overbore. What should my ring gap be? Same as before (.15mm-.35mm, replace at .80mm ?) At which point in the barrel do i measure the gap?

My barrels are ~54.5x

Is my 'wear limit' still .1mm on the overbored cylinder?

Is my piston clearance still .040-.055mm ? At what point in the barrel do I measure this? 19mm from top of cylinder?

I think the answer is 'yes' to my questions, but wanted to confirm

[Craig380]

Hard to tell from the video, could be piston slap or could be a wrist pin bearing.

Measure the ring gap at the BOTTOM of the barrel (below the transfers) as very little wear happens here. Then measure it again 1cm from the TOP of the barrel. The difference between the two ring gap measurements will give you an idea of bore wear.

[Vintageman]

What is the history of your motorcycle? Did you do the over bore and select the piston?

Have you had this for while and issue just showed up? How many miles on 0.5mm OS pistons

In answer to your question about specs - ring gap, piston to cyl clearance, bore out of true wear (i.e. the 0.1mm) were did you get data?.. sounds OK but, search on GT Resources and there are service bulletins with specs. to verify your numbers and how to measure.

Without waiting for answer to my questions about bike's history. I am going to make some assumption.

You do have above normal top end noise? (hard to tell by that vid's sound) These bikes do make a noise versus liquid cooled engines for sure but, idling and under 3000 rpm should not be too bad.

Does the bore have score marks or piston skirt scuffs marks? if so that makes a lot of noise

Ring gap too large tells a lot about wear. Too large piston cyl clearance also makes much piston slap noise?

Is there a ridge at top of bore since rings don't go all the way to top? The ridge is caused by cylinder wear from were the rings do travel versus were the don't reach.

Your bike looks like a GT250A 1976. The piston changed that year and differed from the previous one (like GT380). They had to move to ring pin /peg in the piston that holds the rings in place from rotating about. If the wrong one was bought (most everyone on eBay says that the early piston also works (they supersede numbers forward) in the 76-78 GT250s but ,does not. It will work the other way around (new piston in older bike). They move the ring so the ends would not snag in the extra transfer ports added above the intake port on the GT250A and on. So make sure you have correct piston.

If fast wear, not may miles on new pistons, check for lack of oil (air in oil lines). carb jetting way off too rich, bad crank bent rod or sloppy rod side to side shake. The crank may be out of balance, but my experience is that is the least likely cause.

[belopsky]

I do believe this noise existed from the get-go, after I put in a different ignition (DynaS instead of PVL)

I *was not* able to start the bike w a PVL - needed rollers? I traded it tz375 on this forum

The bike started right up (choke only - 3k RPM idle) then settled down and i would turn the choke off. Would idle at around 1500.

The clickity noise always existed on the right.

I was not the one to do the rebore, perhaps you are right about the piston not being the right one, I am not sure. How can I check to make sure my piston is the correct one..

The bore is good, no scoring marks anywhere.

At what point in the bore do I measure ring gap? Perhaps my ring is worn and I need new rings..I imagine a too lose of ring/too big of ring gap would add to the noise.

As far as general running, it ran pretty rich, particularly at idle.

Once I figure out the ring situation and get the top end back together, i will need to re-evalute timing and tuning of the carb..

[Vintageman]

I wouldn't think ring gap wouldn't make that much noise but, to be honest never verified. a large ring gap would indicate a problem though.

Gap: Put the ring in the bore using piston to square ring up in cylinder then measure gap. Try very top where no ring travel and various points in the bore to see if it gets wider (bore wear).

How much it changes divide that by Pi (3.14159...) and that is difference in cyl diameter. For example if you measure 0.022" min and 0.025" max gap. the out or true of cylinder is about 0.001" [(0.025"- 0.022")/3.14..). I just did the math never did it this way, just theory.

I have used thin feeler changes to get a ball park (+/- 0.001" if your careful) piston to cylinder gap. Largest part of piston is at least and inch up from skirt bottom.

Look at the piston carefully for signs of high spot (aluminum build up) and smooth just them down carefully. Really? no signs of build or marking clues on cylinder liner where the piston may have been riding tighter/harder? The old school way it to take new engine run it in a bit and then tear down it looking for these spots and smoothing them out. It will make engine quieter and less friction.

You see no fine scratch lines going up and down starting at the port edges? This would be a sign of ring snagging ( ports not chamfered etc.).

Does t just the very bottom of skirt show dull wear as if it has been rocking due large piston to cyl gap?

Do you see similar fine lines on piston skirt intake exhaust or both running almost full length?

UPDATE: The correct piston has ring locator pins further a part: about 1.400" between them using calipers. The wrong-old piston has about 0.820" between them.

If all checks out OK and you have a little too much clearance if under say 0.005" it will still run OK but, a little noisy.

Does it run well? That year 250 has good pep but no useful power under 4000 rpm.

[Vintageman]

I updated my previously reply with correct spacing on ring locator pins for the 1976 and up Suzuki GT250A/B/C

[belopsky]

thank you, i will check and update

[tz375]

You mention that the motor was rebored and oversize pistons fitted, but was that a long time ago or recently? Even if it was recent (in terms of miles) it is possible that it was wrongly machined.

I would be tempted to remove the right cylinder and measure bore to piston clearance, but before you do that, remove the head and turn the motor over past TDC and then push down hard on top of the piston and see if it "clicks". Repeat if necessary to confirm.

Then put the piston into the bore and slip feeler gauges between piston and bore to measure the clearance on the for and aft faces with the piston close to BDC.

[belopsky]

Past TDC and push down on piston..where am I looking for the click?
Wouldn't it be a matter of the piston 'moving' left/side/side-to-side inside the bore (laterally), not vertically, if there was too much clearance??

I checked to see if there were any issues with my rod: Took my thumb and forefinger, and pulled up/down on the road. No unusual play there, thankfully

[tz375]

As the motor is turned over top dead center, friction will tend to keep the piston high in the bore as the crank turns and takes up any "slack". If you push down on the piston any play can usually be felt easily.

There is always some front to rear rock at TDC because pistons are not round and the sides are not parallel. Top diameter of a piston is much smaller than the bottom of the skirt when cold. That allows for the fact that the top end gets much hotter and expands more.

OK, so no clicking over TDC. That's good. Next you can either measure the piston diameter and bore size and subtract one from the other, but that is only an option with accurate measuring equipment. Or you slip a piston into the bore at or close to BDC and slide feeler gauges in between the piston and bore on the front or rear faces. That isn't quite as accurate but is pretty close and will reveal if the clearances are acceptable or not.

You would expect to be able to slide a 1.5 thou or 2 thou feeler gauge in there but if a 10 or 12 thou (0.012") goes in, we have a problem.